1. Field of the Invention
The present invention relates to an apparatus and method for performing handover in a communication system. More particularly, the present invention relates to an apparatus and method for performing handover according to a Mobile Neighbor Advertisement (MOB_NBR-ADV) message that a Base Station (BS) broadcasts for the handover.
2. Description of the Related Art
The term “handover” refers to a process of enabling a Mobile Station (MS) to move to a target BS to receive a better service when the quality of a service from a serving BS is degraded. To support the handover, the serving BS periodically broadcasts a MOB_NBR-ADV message including information about neighbor BSs to all MSs within its cell. Using the MOB_NBR-ADV message, the MSs within the service coverage area of the serving BS can obtain status information about BSs within neighbor cells. Therefore, when an MS moves from a serving cell to a neighbor cell, it acquires information about the neighbor BS that the serving BS broadcasts to support handover.
FIG. 1 illustrates a cell configuration in which handover occurs in a conventional communication system.
Referring to FIG. 1, the communication system includes cells 100, 110 and 120 (Cell A, Cell B and Cell C, respectively). First, second and third BSs 101, 111 and 121 (BS1, BS2 and BS3, respectively) manage Cell A, Cell B and Cell C, respectively. BS1 communicates with first and second MSs 103 and 105 (MS1 and MS2, respectively), BS2 communicates with third and fourth MSs 113 and 115 (MS3 and MS4, respectively), and BS3 communicates with fifth and sixth MSs 123 and 125 (MS5 and MS6, respectively).
As illustrated by the dashed line in FIG. 1, MS3 is initially provided service by BS2. If the service from BS2 degrades due to a change in circumstance of MS3, for example due to its movement, a change in propagation environment, an increase in the number of MSs in the serving cell, or any other factor, handover is required for MS3. That is, MS3 needs handover to a target BS that provides a better service than the serving BS, BS2. Thus, MS3 synchronizes itself to neighbor BSs (i.e. BS1 and BS3) indicated by a MOB_NBR-ADV message and scans the neighbor BSs by measuring their channel statuses, based on the MOB_NBR-ADV message and a Mobile Scanning Response (MOB_SCN-RSP) message received from BS2. The scanning is performed sequentially in accordance with a list of the neighbor BSs.
After the scanning, MS3 detects the best BS using the channel status measurements. In FIG. 1, MS3 detects the best BS as BS1 and thus performs handover to BS1.
The MOB_NBR-ADV message, which includes information about all neighbor BSs to which an MS within a cell can perform handover, is broadcast to all MSs within the cell.
However, if more than one BS exists in the cell or BSs operating in different modes co-exist in the same area, the MOB_NBR-ADV message must contain an increased amount of neighbor BS information. The resulting increased message size leads to increased transmission overhead. Moreover, as MSs need to scan more BSs, a longer time is required for the scanning, thereby increasing power consumption for the scanning.
Therefore, a need exists for an improved apparatus and method for performing handover that requires less information for transmission and reduces the amount of power consumed for scanning.